1. Field of the Invention
The present invention relates to a method of controlling clamp force exerted in the pulley of a CVT (Continuously Variable Transmission) composed of a belt and pulleys, and more particularly, to a technology that can improve efficiency of a CVT by minimizing clamp force exerted in a pulley as low as possible.
2. Description of Related Art
CVTs composed of a belt and pulleys can continuously control a transmission ratio by controlling hydraulic pressure applied to a driving pulley and a driven pulley.
Since slip should not be generated between the pulleys and the belt in the CVTs, it is necessary to provide clamp force at an appropriate level in the axial directions of the pulleys; however, when unnecessarily too high hydraulic pressure is supplied, energy is wasted, the efficiency of the CVTs is decreased, and the fuel efficiency of the vehicle is reduced.
Therefore, it is required to find and control the optimum point of the clamp force to prevent slip between the pulleys and the belt and a method of determining the final clamp force by multiplying clamp force theoretically calculated by a safety coefficient, determining the point where slip between the belt and the pulleys starts to be generated as a point where the safety coefficient is 1 to decrease the safety coefficient as low as possible, and reducing the clamp force to the point is used in order to find and control the optimum point in the related art.
However, as shown in FIG. 1, the relationship between the clamp force F and the slip is unclear because reduction of clamp force F and a change of a slip ratio Sr do not make a simple corresponding relationship, but as the clamp force F decreases at a constant ratio, the slip ration Sr nonlinearly changes, such that it is difficult to determine the section where the safety coefficient is 1 and a high-performance and high-accuracy sensor needs to be added to detect and use slip for control.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.